This invention is generally directed to negatively charged colored toner and developer compositions useful in electrophotographic imaging and printing processes. More specifically, the present invention relates to negatively charged colored developer compositions with stable triboelectric characteristics, and excellent admix times containing therein certain polymers, first additive particles, and second additive particles. In one embodiment thus there are provided in accordance with the present invention negatively charged developer compositions comprised of styrene butadiene resin particles, first additive particles, second additive particles, colored pigment particles other than black, and carrier particles which consist of, for example, a core with a coating thereover. The aforementioned developers possess several advantages including stable triboelectric charging values for extended time periods exceeding, for example, 200,000 imaging cycles; improved admix characteristics, that is admix charging times in some instances of less than 60 seconds; and moreover the toner particles can be formulated with desired average particle diameters of from 4 to 9 microns. The aforementione developer compositions of the present invention are particularly useful in electrophotographic printing and imaging methods, especially xerographic processes wherein colored images with acceptable resolution and color intensity are generated. Accordingly, images obtained with the developer compositions of the present invention possess image uniformity, edge sharpness, and also the images are nongrainy.
Colored toner compositions are known; for example, there are illustrated in U.S. Pat. No. 4,604,338 positively charged colored toner compositions comprised of first resin particles; second crosslinked resin particles; colored pigment particles excluding black, and selected from cyan, yellow, magneta, brown, blue, and red; a low molecular weight wax; and certain charge enhancing additives. Further, there are described in U.S. Pat. No. 4,513,074 stable developer compositions comprised of first styrene methacrylate resin particles grafted with, or containing a low molecular weight wax; second resin particles of a styrene, acrylate, acrylonitrile terpolymer; pigment particles; colloidal silica additive particles; fatty acid salt additive particles; and uncoated ferrite carrier particles. In column 7, line 26, of this patent it is indicated that various suitable colorants may be incorporated into the developer, such as carbon black nigrosine dyes, and the like. Moreover, in column 5, line 31, of the U.S. Pat. No. 4,513,074 it is stated that the conductive developers illustrated have a number of suitable desirable properties, including a stable conductivity over extended time periods, wide toner concentration ranges, and insensitivity to certain relative humidities. Imaging advantages are illustrated in column 5, lines 35 to 39. In addition, the developers of the U.S. Pat. No. 4,513,074 possess other advantages, including stable triboelectric charging values, namely for example from about 10 to about 40 microcoulombs per gram, see column 5, lines 40 to 57.
In copending application U.S. Pat. No. 4,737,434 there are consistent high quality colored images with a stable two component developer comprised of first and second different polymer particles and blended flow aid additives. Toner particles with an average diameter of 8.5 microns are disclosed in the aforementioned copending application in Example I, page 10.
Also, in U.S. Pat. No. 4,695,524 there is disclosed a process for generating images with a two component magnetic developer, and wherein the toner composition has an average particle diameter of from about 6 to about 10 microns.
Illustrated in U.S. Pat. No. 4,513,075 are developers comprising a mixture of coated carrier particles, and a toner wherein the size of the toner particles is usually from about 5 to about 30 microns, reference column 4, lines 27 to 30. In column 4 of this patent, it is indicated that in order to make the toner color deep a bluish nigrosine dye is mixed to the binder resin. Moreover, a charge controlling agent can be added to the toner resin, reference column 4, lines 65 to 68, and column 5 of the 075 patent. As carrier particles, there are mentioned in this patent cores coated with a resin comprising a butadiene homopolymer with certain molecular weights, or a mixture of homopolymers and a styrene butadiene copolymer, reference column 3, lines 1 to 8.
Described in U.S. Pat. No. 4,564,573 are toners comprising a binder with at least 60 percent by weight of a styrene butadiene copolymer, which copolymer possesses certain characteristics, including a molecular weight of 100,000 with a ratio of at least 20. In column 8, line 21, of this patent there is disclosed the addition of pigments or dyes as well as other additives, such as components for controlling the electrostatic polarity with specific examples of colorants being outlined at column 8, line 31, including carbon black, aniline blue, chrome yellow, DuPont oil red, and the like. Additionally, in column 8, line 47, it is indicated that magnetic substances may be selected for the preparation of magnetic toners.
Additionally, toner and developer compositions, especially those containing charge enhancing additives, are well known, reference for example U.S. Pats. Nos. 3,893,935; 3,944,493; 4,007,293; 4,079,014 and 4,394,430. Further, there is disclosed in U.S. Pat. No. 4,338,390 developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate substances. A similar disclosure is present in U.S. Pat. No. 4,394,430. Moreover, there are disclosed in U.S. Pat. No. 4,298,672 positively charged toner compositions with resin particles and pigment particles; and as a charge enhancing additive, alkyl pyridinium compounds, inclusive of cetyl pyridinium chloride.
Examples of toner resins described in the prior art include polyamides, epoxies, diolefins, polyurethanes, vinyl resins and polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol. Suitable vinyl resins may be selected including homopolymers or copolymers of two or more vinyl monomers. Typical vinyl monomeric units are styrene, p-chlorostyrene, unsaturated mono-olefins such as ethylene, propylene, butylene, isobutylene and the like; vinyl esters such as esters of monocarboxylic acids including methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methylalpha-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and other similar acrylates; acrylonitrile; methacrylonitrile, acrylimide, vinyl ethers, such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether, and the like; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone; and N-vinyl indole, N-vinyl pyrrolidene, and the like; styrene butadiene copolymers, and mixtures thereof.
As preferred toner resins there can be selected styrene polymers and the esterification products of a dicarboxylic acid, and a diol comprising a diphenol. The aforementioned polyesters are illustrated in U.S. Pat. No. 3,590,000. Other specific preferred toner resins include styrene/methacrylate copolymers, styrene/butadiene copolymers, polyester resins obtained from the reaction of bisphenol A and propylene oxide, followed by the reaction of the resulting product with fumaric acid, branched polyester resins resulting from the reaction of dimethyl terephthalate, 1,3-butanediol, 1,2-propanediol, and pentaerythritol; styrene butadiene copolymers prepared by a suspension polymerization process, reference U.S. Pat. No. 4,558,108, the disclosure of which is totally incorporated herein by reference.
Other representative patents primarily of background interest include U.S. Pat. No. 4,237,257 relating to methods for preparing low molecular weight styrene series polymers useful as toners, which preparation involves the selection of an organic peroxide intitiator; U.S. Pat. No. 4,339,337 relating to a suspension polymerization method for the preparation of magnetic beads from vinyl aromatic polymers, including styrenes, and where benzoyl initiators may be selected, reference column 3, line 17; and U.S. Pat. No. 4,617,249 relating to toners with a crosslinking compound, reference for example column 4, lines 42 to 64.
However, there is a need for new developer compositions that possess certain desirable characteristics, and that are useful in electrophotographic imaging systems. Additionally, there is a need for negatively charged colored developer compositions with stable triboelectric charging values and improved admix charging times. Furthermore, there is a need for negatively charged colored developer compositions wherein toner particles with an average particle diameter of from 4 to 9 microns can be formulated thereby permitting the advantages indicated herein. In addition, there is a need for resins useful for the formulation of toner compositions with specific diameters that possess desirable mechanical properties, stable electrical properties, excellent fusing characteristics, and acceptable release properties. Moreover, there is a need for developer compositions containing therein toner components illustrated herein, and carrier particles. There is also a need for imaging and printing methods wherein colored images of excellent resolution with consistent high copy quality are obtained for an extended number of imaging cycles exceeding 200,000 in some instances.